In recent years, in the magnetic disk apparatus, a technique for writing data to the magnetic disk at high density has been developed. This technique is called a shingled write recording method for writing data so that neighboring tracks on a magnetic disk overlap each other. In the shingled write recording method, since the neighboring tracks overlap each other, the number of tracks which are recordable per the magnetic disk can be increased, and data can be written at a higher density.
Also, a so-called inter-track interference (ITI) cancellation technique has been developed. With this technique, upon reading data which have been written to the magnetic disk using the shingled write recording method, noise can be canceled using data written to a track which neighbors the track currently being read.
While data are written to a given track using the shingled write recording method, they are unexpectedly written at positions outside the currently written track because of influences such as vibration, thus causing off-track errors. After the off-track error has occurred, processing for writing data (write processing) must be interrupted until an on-track state, that is, the state where allow data to be written to the magnetic disk as a result of tracking control.
Since it is difficult to read data which have been written to an area of the magnetic disk where an off-track error has occurred, those data must be rewritten to the magnetic disk. Furthermore, when data are overwritten in the area where the off-track error has occurred, the influence of magnetic interference on the neighboring tracks often becomes greater.